Rods "Spaceship" Scratch built Plasma Cutter build

Andy, Thanks for your interest. Yes 70mm bore. Its some obscure Chinese brand that we had never heard of. We have it apart waiting for a spindle bearing. When it was at full speed, it was roaring like a jumbo jet! We have a choice of spending $540 for it and have it overnight or paying $150 ex China and waiting 3 weeks.. Also have to sort out the coolant and rapid feed as they are not working.

Speaking of obscure Chinese brands, have you ever heard of Mitutogo? The reason I ask is a new dial indicator arrived today.

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I bought the Chinese Counterfeit on the right years ago for about $10 before I knew what a Mitutoyo was. About 4 years later, I realised the play on words with the Mitutogo brand on it. The fake had a worn dovetail mounting clamp so I could not hold it in my mill easily but the mechanism is still in perfect working order. Now I've replaced it, I thought to give it a squeeze in a vice and its fixed. Makes me wonder why I spent $60 on a new one :S

The new one on the left is the genuine article. Pretty good copy don't you think?

rodw wrote: I bought the Chinese Counterfeit on the right years ago for about $10 before I knew what a Mitutoyo was. About 4 years later, I realised the play on words with the Mitutogo brand on it.

Is it a play on words, or just that the counterfeiter was unfamiliar with the latin script and actually got it wrong?

Andy, even I am not old enough to remember anything about Latin so unless the invention dates back to Confucian times, I suspect given every other detail is correct, our Chinese friend knew exactly what he was doing!

Anyway, I had a bit of a revelation today after re-reading this thread on the Everlast forum.
www.everlastgenerators.com/forums/showth...arc-voltage-dividers

You see my Everlast plasma cutter has three choices for voltage output (Raw voltage, 50:1 and 16:1). I thought I would have to use the 50:1 divider with the 10 volt version of the which meant at say 300V, the max scale reading would only be 6 volts so resolution would not be that great. But Post #5 changed all that. All I have to do is to use a 2:1 voltage divider to drop the 16:1 divider from a max scale of 18.75 volts to 9.375 volts or pretty much full scale. I think I could even fit the components inside the cable backshell. I will take their advice and take some measurements first.

So the two resistors need to have an identical value to halve the voltage. I get that part.

The thing I don't understand with voltage dividers is what resistance value should be used. Can somebody suggest a value to use?

There are several software for smartphones that can do electronic calculations, some do voltage dividers, but i do not know any names as i never used them, just seen them on playstore.
Basicaly you need to know the voltage and the current that needs to run through them, that will in turn determine the values and the power rating.
Roughly, 20V and 10mA should do fine, so 2kOhm total, divided in half makes for 2 resistors of 1kOhm, power disipation of 200mW so even small resistors will do fine. Just to be on the safe side i would use 1/2W resistors, a 1kOhm and a 1.2kOhm as that would result in something like 9V output at full 300V on the plasma. I have seen some that go up to 280V with no load.

Tommy, Thanks so much for that info. It was very helpful and informative.

Please read the "Extending Input Range" section of the THCAD manual
Extending the input range is not done with a divider but rather a series resistor